The automaker did not say now much the recall would cost and it was not clear if the faults stemmed from Toyota's suppliers or its manufacturing process. "We sincerely apologize to our customers for the inconvenience and concern brought by this recall announcement," Toyota added in a statement.

Large scale recalls have become more common in recent years as automakers move to fix defects quickly after Toyota was forced to recall more than 9 million vehicles to address sticky accelerators linked to fatal accidents.

Read More Ford recalls nearly 435,000 vehicles

That recall, which forced Toyota President Akio Toyoda to testify in U.S. Congress, weighed heavily on the company's sales and reputation, culminating in a record $1.2 billion settlement agreed only last month, with more private lawsuits still pending.

Toyota said some 3.5 million vehicles were being recalled to replace a spiral cable that could be damaged when the steering wheel is turned, causing the air bag to fail to activate in the event of a crash. About half of those vehicles, produced between April 2004 and December 2010, are in North America.

Another 2.32 million three-door models made between January 2005 and August 2010 are being recalled to check the rails that could cause the seat to slide forward in a crash.

The 6.39 million vehicle recall is the largest announced on a single day for Toyota since October 2012, when it called back 7.43 million Yaris, Corolla and other models to fix faulty power window switches.

It also comes as rival GM is under investigation for failing for years to act on a known ignition switch defect linked to a dozen deaths. The company has recalled 1.6 million vehicles over the issue.

Chrysleralso said last week it was recalling nearly 870,000 sport utility vehicles to fix a brake problem.

[Correction: An earlier version of this story had 6.58 millon vehicles recalled which Reuters has since issued a correction]